Drivers of amphibian richness in European ponds

Amphibians are commonly occurring inhabitants of most lentic freshwater ecosystems, yet their global populations are in alarming decline. Ponds in particular play a crucial role in supporting amphibian biodiversity. In this study, we identified the main drivers influencing amphibian species richness by conducting a comprehensive ecological characterization in 201 ponds across seven European countries spanning a large latitudinal and longitudinal gradient. The amphibian species richness in each of these ponds was assessed using environmental DNA metabarcoding on water samples. The relative influence of climatic, local abiotic and biotic, and land use variables on variation in species richness across ponds was quantified using Boosted Regression Trees. Our results suggest that local factors, particularly chlorophyll-a concentration, but also pond area and depth, are the main drivers of amphibian richness, together with climatic variables such as annual mean precipitation and temperature. The highest richness was observed in low-nutrient, fishless, intermediate-sized, shallow ponds, located in warmer regions with higher precipitation rates. These potential drivers of amphibian richness should be considered in the planning and implementation of amphibian conservation and management actions. Methods Sampling Sites: 201 ponds were sampled across Belgium, Denmark, Germany, Spain, Switzerland, the United Kingdom, and Turkey. eDNA Collection: Water samples were collected and analyzed using environmental DNA metabarcoding techniques. Variables Measured: Climatic (e.g., temperature, precipitation), land use, abiotic (e.g., pond depth, nutrient concentrations), and biotic factors (e.g., vegetation, fish richness). Detailed methods are provided in the associated manuscript.